A.2 Health Reporting Areas
A.2.1 Introduction
Resolving geographic units that do not neatly coincide is a common problem in spatial data analysis. The method outline here attempts to conflate King County Health Reporting Areas (HRAs) to US Census tracts. In the cases where a given tract is entirely within an HRA, that tract receives the HRA’s unique identifier (HRA_ID). On the other hand, in cases where a given tract overlaps multiple HRAs, block-level census data is used to determine which HRA ID to assign to the tract.
A.2.2 Census Block Counts
This method provides three alternatives of block-level counts that can be used:
| Count Type | Variable ID | Source |
|---|---|---|
| Population | POP |
Table P1, U.S. Census Bureau, 2010 Census |
| Housing Units | HU |
Table H1, U.S. Census Bureau, 2010 Census |
| Population in Housing Units | HUPOP |
Table H10, U.S. Census Bureau, 2010 Census |
A.2.3 The Algorithm
The following actions are performed in this method:
- Centroids of the census block polygons are calculated (
class = SpatialPointsDataFrame) - HRA IDs are passed to the block centroid using a spatial overlay method (
sp::over()) - Blocks are aggregated into tracts and the count variables (
POP,HU,POPHU) are summed - For each count variable, the HRA ID with the highest sum is assigned to each tract
After running the assignment algorithm, it is clear that the POP and POPHU variables result in the same HRA assignments. HU differs from the other two variables in three of the tracts:
| GEOID_TR | HRA_POP | HRA_POPHU | HRA_HU |
|---|---|---|---|
| 53033022202 | Kirkland North | Kirkland North | Kirkland |
| 53033025001 | Bellevue-South | Bellevue-South | Newcastle/Four Creeks |
| 53033028801 | SeaTac/Tukwila | SeaTac/Tukwila | Des Moines/Normandy Park |